Method of preparing molds



1966 R. w. KIRKPATRICK 3,263,287

METHOD OF PREPARING MOLDS Filed Nov. 5, 1964 I I/// @SSI Area A Area 8 N(N 3 8 SPEC/F/C HUM/D/TY Grains //b of air I l 1 l l l 50 60 70 800/I300 I 0 I I HVVE-NTOR RICHARD w K/RKPATR/CK A lmrney United StatesPatent "ice 3,263,287 METHOD OF PREPARING MOLDS Richard W. Kirkpatrick,North Canton, Ohio, assignor to United States Steel Corporation, acorporation of Delaware Filed Nov. 3, 1964, Ser. No. 408,578 '4 Claims.(Cl. 22-192) This invention relates to an improved method of preparingmolds used in the manufacture of cast iron rolls.

A conventional mold used in forming a cast iron roll includes a castiron chill in which the roll body is formed, and a sand drag and cope inwhich necks are formed at opposite ends of the body. The mold is placedin an upright position with the drag at the bottom and the cope at thetop, and molten iron poured through a gate in the drag. The iron swirlsas it rises through the mold to fill the chill and cope. Contact withthe chill rapidly cools the outside of the body to produce a hard case.The remainder of the roll casting cools more slowly to providetoughness.

The chill must be preheated above ambient temperature before the molteniron is introduced to prevent its cracking because of the extremetemperature ditference. Commonly the chill is preheated to about 600 to800 F., and the molten iron poured at about 2800 F. It is essential thatthe chill have a rust-free surface, since any rust spots leave defectsin the roll casting. The cope and drag are formed with sand whichcontains about 8 to 8.5 percent moisture. Before the molten iron ispoured, the sand must be dried almost completely and it must be free ofdefects such as blow holes caused by overly rapid vaporization ofmoisture during the drying operation. Thus it is necessary to heat boththe metal and sand parts of the mold under controlled conditions whichdo not rust the metal, and which fully dry the sand without producingdefects. Previous practice has been to heat the mold parts inrecirculating-type heaters in which products of combustion do notcontact the parts directly. Direct-fired heaters are more efficient, buttheir use produced rust spots on the chills and defects in the sand.

An object of the present invention is to provide an improved method ofpreparing molds in which both the metal and sand parts of the mold areheated by direct firing without damaging the parts.

A more specific object is to provide a method of the foregoing type inwhich the parts are heated first at a relatively low temperature toavoid moisture condensation thereon and later at a relatively hightemperature to condition them for receiving molten iron.

In the drawing:

FIGURE 1 is a vertical sectional view of a heating apparatus with whichI can practice the method of the present invention; and

FIGURE 2 is a graph showing the relation between temperature andhumidity in the apparatus.

FIGURE 1 shows a heating apparatus which includes a direct-fired chamber10, a door 12 at the front of the chamber, a track .13 extending intothe chamber through the door, burners 14 at the back of the chamber, anda flue 15. Mold parts M to be heated are placed on the truck 16 whichenters and leaves the chamber along the track. A blower 17 suppliescombustion air at constant volume to the burners through a duct 18 whichcontains a butterfly valve 19. Gaseous fuel reaches the burners througha line 20, which contains a motorized regulating valve 21. I mount athermocouple 22 in the chamber and connect the thermocouple to anautomatic temperature controller 2 3. I connect the controller to themotor which operates the fuel-regulating valve 21. The controller has anadjustment knob 24, which I can Patented August 2, 1966 set to anytemperature I wish to maintain in the chamber. The controller thenautomatically adjusts valve 2 1 to admit fuel in the proper volume tohold this temperature, as known in the art. By varying the ratio offuel-to-air in this manner, I can maintain a flame temperature anywherefrom about 300 to 2200 F. The products of combustion in the chamber arein direct contact with the mold parts M.

The mold parts M are at ambient temperature when I place them in thechamber 10. I turn on the burners and set the fuel supply to maintain aflame temperature in the range of about 300 to 325 F. I set thetemperature controller 23 to maintain a chamber temperature in the rangeof about 200 to 220 F., as registered at the thermocouple 22. When thechamber is cold, the temperature controller would tend to allow a highflame temperature until the chamber reaches the temperature for whichthe controller is set. Hence I further limit the fuel supply at thebeginning of the cycle to prevent excessive flame temperature. Underthese conditions the parts heat slowly and are dried. The products ofcombustion are at a sufiiciently low concentration that moisture thereindoes not condense on the surface of a chill. As FIGURE 2 showsgraphic-ally, the apparatus is operating in Area B below the saturationcurve. Likewise there is no drastic heat applied to sand parts, such asmight cause unduly rapid vaporization of the moisture therein andresultant defects. I continue to heat the mold parts under theseconditions for about four hours in order to bring them uniformly to atemperature of about 200 to 220 F. Thereafter I change the setting ofthe temperature controller 23 to maintain a chamber temperature of about600 to 800 F. I heat the parts at the latter temperature for about eighthours, after which they are uniformly at the temperature for pouring andproperly dried. For convenience I can operate the controller 23automatically by using a timer to change its setting.

From the foregoing description it is seen that my invention affords asimple effective method of preparing molds for forming cast iron rolls.The main difficulty in heating chills in a direct-fired chamber has beenthat moisture formed as a combustion product condenses on the chill at astart of the cycle. Such moisture causes rust spots which subsequentlylead to a defective casting. I overcome this difficulty by maintainingthe combustion products at a low concentration until the chill is at atemperature above the dew point. The slow heating also avoids damage tothe sand parts of the mold, as already explained.

While I have shown and described only a single embodiment of myinvention, it is apparent that modifications may arise. Therefore, I donot wish to be limited to the disclosure set forth but only by the scopeof the appended claims.

I claim:

1. A method of preparing mold parts for use in forming cast iron rollscomprising placing the parts at ambient temperature in a direct-firedheating chamber, burning gaseous fuel in air in said chamber with theproducts of combustion directly contacting the parts, setting the ratioof fuel-to-air at a level which maintains a flame temperature of about300 to 325 F. and a chamber temperature of about 200 to 220 F. for aboutfour hours, and changing the ratio of fuel-to-air to a level whichmaintains the chamber temperature at about 600 to 800 F. for about eighthours, whereby the parts heat slowly until they reach a temperatureabove the dew point and thereafter heat to a temperature for receivingmolten iron.

2. A method as defined in claim 1 in which the parts include a cast ironchill and in which the slow heating limits the products of combustion toa concentration insutficient for moisture in the products to condense onthe surface of the chill until the surface reaches a temperature abovethe dew point.

3. A method as defined in claim 1 in which the parts 5 include sandparts initially containing 8 to 8.5 percent moisture and in which theslow heating prevents overly rapid vaporization of the moisture.

4. A method as defined in claim 1 in which the volume of air introducedto the chamber remains constant and the ratio is changed by regulatingthe volume of fuel.

References Cited by the Examiner UNITED STATES PATENTS 1,335,222 3/1920Davis 22-87 2,258,515 10/1941 Mowat 263-52X 2,543,388 2/1951 Urquhart263-52 J. SPENCER OV-ERHOLSER, Primary Examiner.

E. MAR, Assistant Examiner.

1. A METHOD OF PREPARING MOLD PARTS FOR USE IN FORMING CAST ORON ROLLSCOMPRISING PLACING THE PARTS AT AMBIENT TAMPERATURE IN A DIRECT-FIREDHEATING CHAMBERS, BURNING GASEOUS FUEL IN AIR IN SAID CHAMBER WITH THEPRODUCTS OF COMBUSTION DIRECTLY CONTACTING THE PARTS, SETTING THE RATIOOF FUEL-TO-AIR AT A LEVEL WHICH MAINTAINS A FLAME TEMPERATURE OF ABOUT300* TO 325*F. AND A CHAMBER TEMPERATURE OF ABOUT 200* TO 220*F. FORABOUT FOUR HOURS, AND CHANGING THE RATIO OF FUEL-TO-AIR TO A LEVEL WHICHMAINTAINS THE CHAMBER TEMPERATURE AT ABOUT 600* TO 800*F. FOR ABOUTEIGHT HOURS, WHEREBY THE PARTS HEAT SLOWLY UNTIL THEY REACH ATEMPERATURE ABOVE THE DEW POINT AND THEREAFTER HEAT TO A TEMPERATURE FORRECEIVING MOLTEN IRON.